For electrical engineers only: I have a pressure transmitter...?
Anyway i made sure that there is no ground loop so i grounded the shiled at only one terminal
So what causes this jump?
This is not a transient effect ,it lasta as long as the motor is running
The 24V supply is coming through the main supply to the motor
When motor is off ,the Volatge is 22.4V and when motor starts it goes to 24.2
It is a new installation
This is not due to pressure surge it is just realted to motor start
in addition,is 200mA AC current in the shield normal?
By the way,in the system there are several transmitters ,but this problem happens only for two transmitters of the SAME TYPE
Answer:
As you said that this is not due to the pressure of the pump discharge header. So there are possiblities that there is induce voltage on the transmission line of the TX due to the high power lines of the pumps. Also there is possibility that this type of TX is so sensitive to the electromagnetic noise and induced stray voltages on its line.
Advice that, provide separate conduit system for this type of TX and keep it away from high voltage lines.
Try http://www.eng-tips.com/
The PT measures pump pressure right?
When the pump is off you read no pressure (4mA).
You turn the pump on and the PT measures pressure (8mA) . Which is 25% of full scale. What is the problem? The question is extreamly vague.
i will bet money that this is feeding back the pressure of the pump, but you have the pressure transducer too close to the pump outlet. Move it down stream if measuring system pressure, and add an accumulator to the fluid system to stableize readings...the pump is going to vary much more dramaticly with changes to load. especially startup.
isolate 24v ac signal from the 4-20 ma out put, besides there shouldn't be a 200 ma ac current in the shield. be sure that the 24v supply to your transmitter wont be affected by the motor start up.
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